Wyeth has notified healthcare professionals of revisions to the Rapamune (sirolimus) Prescribing Information regarding changes in the performance of an immunoassay used for therapeutic drug monitoring (TDM) of sirolimus. It has come to Wyeth’s attention, that the IMx immunoassay platform may yield results with a negative bias relative to the reference assay HLPC/MS/MS.  This may vary from one laboratory to another and may also be affected by whether fresh or frozen blood samples are utilized. Switching between platforms, whether between immunoassay platforms or between immunoassay and HPLC, can produce differing results that may be clinically significant.

Wyeth is advising healthcare professionals to determine: 1) which assay is being used in their laboratory; 2) if there is any change to the assay used; 3) if there is a change to the laboratory’s reference range and/or a subsequent change to the institution’s or referring center’s recommended range for sirolimus. Adjustment to the targeted therapeutic range must be made with a detailed knowledge of the site-specific assay used.

Rapamune oral solution and tablets are indicated for the prophylaxis of organ rejection patients ≥13 years of age receiving renal transplants.

For more information visit www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm197059.htm.